2O3 Composites Research Articles

Copper/cobalt-doped LaMnO3 perovskite oxide as a bifunctional catalyst for rechargeable Li-O2 batteries

Copper/cobalt-doped perovskite oxide LaMn0.8M0.2O3 (M = Cu, Co) composites are synthesized through gel combustion with urea as the chelating agent and fuel. Both LaMn0.8Cu0.2O3 and LaMn0.8Co0.2O3 exhibit better catalytic performances for OER and ORR than LaMnO3 in alkaline media due to the abundance of oxygen vacancies and Mn4+ caused by the substitution of different valence elements. When used as a cathode catalyst in Li-O2 batteries, LaMn0.8Co0.2O3 can perform 91 stable cycles at 100 mA g−1 and the discharge specific capacity can reach up to 9620 mA h g−1 at 500 mA g−1. LaMn0.8Co0.2O3 has a longer cycle life and larger discharge capacity compared to LaMnO3 and LaMn0.8Cu0.2O3.

Continuous Composition Spread and Electrochemical Studies of Low Cobalt Content Li(Ni,Mn,Co)O2 Cathode Materials

Many scientific efforts have been undertaken toward reducing the Co content in LiMn1/3Ni1/3Co1/3O2 cathode materials for thin-film batteries. In this study, we present cathodes with a wide range of Li(Ni, Mn, Co)O2 compositions to determine the material with the best electrochemical performance by changing the ratio of Ni to Mn at a fixed 0.1 at.% of Co by the continuous composition spread sputtering method. The cathode composition measurements by Rutherford backscattering spectroscopy show that the best electrochemical performance is obtained for a composition of Ni:Mn:Co = 19:71:10. The reasons for this improved electrochemical performance are further investigated by X-ray diffraction, electrochemical impedance spectroscopy, Fourier-transform infrared spectroscopy, and X-ray absorption near edge spectroscopy.

LiCoxNi1−xO2 with high dielectric and microwave absorption performance in X-band

Abstract In this study, we initially report the effect of lithium cobalt oxide (LiCoO2) doped with different Ni ion contents on the dielectric and microwave absorption properties. Pure phases of LiCoxNi1−xO2 (x = 0.2, 0.4, 0.6 and 0.8) have been synthesized using a solid-state reaction. Both the permittivity and permeability values of the LiCoxNi1−xO2 composites distinctly shifted with increasing Ni-doping content. The result indicates that the LiCo0.4Ni0.6O2 composite exhibits appropriate permittivity, which can be attributed to the increasing Ni ion distribution and distortion lattice volume. Further, the eʹ and eʹʹ values of LiCo0.4Ni0.6O2 composite are 3.5 and 35 times higher than that of the LiCo0.8Ni0.2O2 composite. The minimum reflection loss and wide absorption band can be obtained by calculating reflection loss of the LiCoxNi1−xO2 composites with various compositions (x) and thicknesses. The optimum reflection loss value of the LiCo0.4Ni0.6O2 composite is −46 dB with a thickness of 2.6 mm at 8.63 GHz, and the absorber bandwidth (RL

Effects of local distortion on the electrical properties of lead free perovskite-type electro-ceramics Ba1-xCaxTi0.9Zr0.1O3

The electro-ceramic industry has focused their attention on replacing lead-based materials due to their toxic effects and unfavourable environment impact. Barium titanate doped with calcium and zirconium denoted in this work as BCZT is a well-known perovskite-type solid solution. In particular, Ba1-xCaxTi0.9Zr0.1O3 (where x = 0, 0.1 and 0.15) compositions are located near the so called morphotropic phase boundary (MPB): coexistence of ferroelectric phases. This work shows the relationship between the crystal and electronic structure with the dielectric and piezo-ferroelectric properties. The high-resolution X-ray diffraction (HR-XRD) results suggest the coexistence of tetragonal and rhombohedral phases over the obtained compositions. The dielectric analysis indicates a relaxor behaviour with a Curie temperature in a range of 100-120°C. Piezoelectric and ferroelectric evaluation complement the electrical characterization for these compositions. Micro–X-ray absorption near edge spectroscopy (μ-XANES) was performed to monitor possible changes of electronic structure profile due to the local distortions as Ca2+ increases.

Effect of MoO3 on the Catalytic Properties of NiO/Al2O3 in the Carbon Dioxide Conversion of Methane

The effect of molybdenum oxide as modifying additive on the catalytic properties of the catalyst NiO/Al2O3 obtained by the “solution combustion” method in the carbon dioxide conversion of methane was studied. It was established that the addition of 1 wt.% MoO3 to the 3 wt.% NiO/γ-Al2O3 composition leads to an increase in the specific surface area of the catalyst and the mobility of the surface oxygen, resulting in increased catalyst activity and resistance to carbonization.

High Lithium Ion Transport Through rGO-Wrapped LiNi0.6Co0.2Mn0.2O2 Cathode Material for High-Rate Capable Lithium Ion Batteries.

In this work, we show an effective ultrasonication-assisted self-assembly method under surfactant solution for a high-rate capable rGO-wrapped LiNi0.6Co0.2Mn0.2O2 (Ni-rich cathode material) composite. Ultrasonication indicates the pulverization of the aggregated bulk material into primary nanoparticles, which is effectively beneficial for synthesizing a homogeneous wrapped composite with rGO. The cathode composite demonstrates a high initial capacity of 196.5 mAh/g and a stable capacity retention of 83% after 100 cycles at a current density of 20 mA/g. The high-rate capability shows 195 and 140 mAh/g at a current density of 50 and 500 mA/g, respectively. The high-rate capable performance is attributed to the rapid lithium ion diffusivity, which is confirmed by calculating the transformation kinetics of the lithium ion by galvanostatic intermittent titration technique (GITT) measurement. The lithium ion diffusion rate (DLi) of the rGO-wrapped LiNi0.6Co0.2Mn0.2O2 composite is ca. 20 times higher than that of lithium metal plating on anode during the charge procedure, and this is demonstrated by the high interconnection of LiNi0.6Co0.2Mn0.2O2 and conductive rGO sheets in the composite. The unique transformation kinetics of the cathode composite presented in this study is an unprecedented verification example of a high-rate capable Ni-rich cathode material wrapped by highly conductive rGO sheets.

Synthesis of high performance nano-over-lithiated oxide coated LiNi0.6Co0.2Mn0.2O2 from spent lithium ion batteries

The widely usage of LiNi1-x-yCoxMnyO2 (NCM, here 1-x-y≤0.5) batteries makes their recovering and recycling urgent requirements. Here, a novel efficient and environmentally friendly recycling process have been developed to synthesis high performance NCM materials from spent NCM batteries. The recovery process comprises battery dismantling process, spent cathode separation and purification process, precipitation process and a heat treatment process. In the typical Mn2+, Co2+, and Ni2+ solutions are introduced to form Mn0.54Ni0.13Co0.13(OH)1.6 homogeneously coated precursor. The final Li1.20Mn0.54Ni0.13Co0.13O2(LLO) coated LiNi0.6Co0.2Mn0.2O2(NCM622) composite is obtained by commonly used heat treatment. LLO modification recovers the electrochemical activity of spent NCM622 pronouncedly even better than the reference commercialized NCM622. 1% LLO active materials show discharge capacities of 178.2 mAh g−1 at 0.2 C rate and display a superior cycling performance with 98.4% capacity retention after 100 cycles.

Facile Preparation of Snowflake-Like MnO2 @NiCo2 O4 Composites for Highly Efficient Electromagnetic Wave Absorption.

Snowflake-like MnO2 @NiCo2 O4 composites were successfully fabricated by employing crossed snowflake-like MnO2 nanorods as cores and one-dimensional (1D) NiCo2 O4 nanoneedles as shells. Impressively, the MnO2 @NiCo2 O4 composites exhibited a highly efficient electromagnetic wave (EMW) absorbing capability, and the minimum reflection loss (RL) value reached -58.4 dB at 6.8 GHz for a thickness of 4.0 mm. The reasons for the improved EMW absorption capability of snowflake-like MnO2 @NiCo2 O4 composites were analyzed. The unique core-shell structure, good impedance matching, and high dielectric loss were all found to be important contributors. Moreover, the interfacial polarization mainly stemmed from the heterostructure, a microcurrent generated from the 1D MnO2 nanorods and NiCo2 O4 nanoneedles under alternating electromagnetic fields, and the synergistic effect from the different components were all beneficial to improve the EMW absorption performance. These results demonstrated that snowflake-like MnO2 @NiCo2 O4 composites could be utilized as promising materials for practical EMW absorbing applications.

Co3O4/α-Fe2O3 catalyzed oxidative degradation of gaseous benzene: Preparation, characterization and its catalytic properties

Cobalt oxide/hematite (Co3O4/α-Fe2O3) composites were synthesized by using goethite as precursor via co-precipitation calcination method and employed in the catalytic degradation of benzene. The catalysts properties of the Co3O4/α-Fe2O3 composites were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption measurement (BET), X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR) techniques, respectively. The results showed that the Co3O4/α-Fe2O3 composite had excellent catalytic oxidative performance on catalytic degradation of gaseous benzene, and its catalytic activity were influenced markedly by the ratio of Co3O4 and the calcination temperature. When the composite catalyst with the Co/Fe molar ratio of 0.6, calcined temperature at 500 °C and benzene initial concentration was 1000 mg/m3, the catalyzed oxidative temperature which benzene completely conversion and 91.7% CO2 selectivity was 400 °C. Large specific surface area, abundant surface oxygen species and strong redox properties which were ascribed to the interaction between Fe2O3 and Co3O4 play an important role in the catalyzed oxidative degradation of benzene.

Evolution of dielectric properties in the (1−x) PbFe0.5Nb0.5O3–xBaFe0.5Nb0.5O3 solid solution system

Temperature dependences of the dielectric permittivity e of (1−x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 solid solution ceramics at 100 Hz–1 MHz have been studied in the 12–500 K temperature range. To lower the conductivity values and exclude the corresponding relaxations, 1 wt% of Li2CO3 was added to the starting mixture of oxides. It was found that Li-doping is effective in lowering the conductivity only for compositions with x ≤ 0.5. T he permittivity–temperature dependences of the (1−x)PbFe0.5Nb0.5O3–xBaFe0.5Nb0.5O3 compositions were found to change, as x grows, from relatively sharp frequency-independent maxima typical of usual ferroelectrics to the diffused and frequency-dependent maxima typical of relaxors and then to the saturated at low temperatures and frequency-independent e(T) curves typical of incipient ferroelectrics and at last, to the step-like frequency-dependent e(T) curves known for the dielectrics with Maxwell–Wagner-type polarization. The e value of BaFe0.5Nb0.5O3 at 20 K measured at 1 MHz does not exceed 30. The character of the evolution of dielectric properties in the (1−x)PbFe0.5Nb0.5O3–x BaFe0.5Nb0.5O3 system and low e value of BaFe0.5Nb0.5O3 implies that BaFe0.5Nb0.5O3 is a paraelectric rather than ferroelectric relaxor.

Structure, Linear Thermal Expansion Coefficient, and Electrical Conductivity of Y0.9Ca0.1Cr1 – уCoуO3 (у = 0–0.9) Perovskites

The structure, thermal expansion coefficient, and electrical conductivity of Y0.9Ca0.1Cr1 – уCoуO3 (у = 0–0.9) compounds with the perovskite structure have been investigated in air in the temperature range of 100–1000°С. The linear thermal expansion coefficient of Y1 – хCaхCr1 – уCoуO3 lies in the range of (8.77–16.1) × 10–6 K–1. The maximum electrical conductivity is attained for the Y0.9Ca0.1Cr0.6Co0.4O3 composition. It is shown that the electrical conductivity at low (25–270°С) temperatures and weak substitution of cobalt for chromium is mainly due to the hopping of one electron hole from Cr4+ to Cr3+. At high (565–1000°С) temperatures and cobalt contents, this conductivity mechanism is supplemented with the conductivity caused by the hopping of an electron hole from Cо3+ to Cо2+.

Electrocaloric behavior of Ba0.85Ca0.15Zr0.1Ti0.88Sn0.02O3 cement composites

Abstract A thrust for looking multifunctional materials for applications in civil engineering structures has attracted interest among researchers across the globe. Cement based Ba0.85Ca0.15Zr0.1Ti0.88Sn0.02O3 (BCZT−Sn) composites were prepared for electrocaloric applications with varying BCZT−Sn to cement ratio. Hysteresis loops showed some signature of saturation in cement composites. However, loops of pure sample were saturated due to its ferroelectric nature. Furthermore, these composites were explored for the first time in solid state refrigeration technology namely electrocaloric effect (ECE). Peak electrocaloric performance shows an adiabatic temperature changes of 0.71, 0.64 and 0.50 K and isothermal entropy changes of 0.86, 0.80 and 0.65 J/(kg·K) for BCZT−Sn, 10% and 15% cement composites, respectively, under application of 0−29 kV/cm electric field. The adiabatic temperature change in cement based composites is comparable with that of the BCZT−Sn ferroelectric ceramics. Furthermore, the dielectric constant (er) of composites with different ceramic contents at room temperature reveals that dielectric constant increases with an increase in BCZT−Sn proportion in composites. These cement based BCZT−Sn composite materials may be used in solid state refrigeration as they are fairly competitive with the pristine sample.

Magnetic field control of electric properties in gadolinium doped BaTiO3 –CoFe2O4 particulate multiferroic composites

In functional materials such as multiferroics, the emergent tunable physical properties usually arise at the interface of complex heterostructures due to the interplay between various degrees of freedom. To explore such properties in the multiferroic materials, these should generate high capacitance upon the application of magnetic fields, which is the prime requirement for next generation four state memory devices. Taking into account the multifunctional behaviour of multiferroic composites, in this article, an attempt has been done to synthesize and probe the various functional properties of the (1 − x) Ba0.95Gd0.05TiO3-xCoGd0.1Fe1.9O4 (x = 0.03, 0.06 and 0.09) biphasic particulate composites. X-ray diffraction studies revealed decrease in tetragonality of ferroelectric Ba0.95Gd0.05TiO3 phase, with the increase in the ferrimagnetic CoGd0.1Fe1.9O4 phase in composites, which is responsible for the enhanced magnetodielectric behaviour. An increase in dielectric constant and a drop in transition temperatures were observed by incorporating Gd in the composites. Asymmetric and rounded ferroelectric hysteresis loops were observed due to high conductivity of CoGd0.1Fe1.9O4 phase in composites. From magnetic studies, it was confirmed that CoGd0.1Fe1.9O4 phase and composites are single and multidomain structured respectively. As all the composites have multidomain, so Law of Approach analysis was adopted to calculate magnetocrystalline anisotropy. The electric properties were tuned by the application of magnetic field, assuring interface coupling between two ferroic phases, the nature of whom was confirmed by Ginzburg–Landau theory. The simultaneous existence of electric, magnetic properties and the interface coupling between two ferroic phases proves the applicability of such particulate composite for multifunctional applications.

RGO/MoS2/Ce0.75Zr0.25O2 electro-Fenton cathode with higher matching and complementarity for efficient degradation of ciprofloxacin

Abstract It’s urgent to develop effective methods to remove antibiotics in environment, especially in drinking water. In this work, RGO/MoS2/Ce0.75Zr0.25O2 composite was prepared by hydrothermal self-assembly method and firstly used as cathode to degrade ciprofloxacin in electro-Fenton system. The removal of ciprofloxacin reached 100% within 5 h, and the mineralization rate achieved 77.1% in 3 h. The optimal degradation conditions were investigated, and the composite was fully characterized by SEM, XRD, BET, XPS, CV and EIS. The results showed that MoS2 and Ce0.75Zr0.25O2 nanoparticles were introduced onto RGO nanosheets successfully. Compared to RGO and RGO/MoS2 composites, the effective degradation performance of RGO/MoS2/Ce0.75Zr0.25O2 cathode was mainly associated with the enhanced electrochemical activities by doping MoS2, heterogeneous catalysis of Ce3+/Ce4+ on decomposition of H2O2, improved oxygen storage capacity owing to the formation of ceria-zirconia solid solution, and effective electro-absorption of RGO. Analysis of H2O2 production and hydroxyl free radicals indicated the predominated role of OH in the electro-Fenton process. The degradation intermediates and the possible degradation mechanism were investigated in detail.

Investigation of biomass conversion on a moving grate by pyrolysis gas analysis and fuel bed modelling

Abstract A profound understanding of the fuel conversion on a grate boiler is crucial for an optimised boiler operation with a minimised pollutant emission. This work presents gas measurements and numeric simulations of a 150 kW moving grate boiler. The fuel bed model considers drying, pyrolysis and gasification. In the experiments, temperature profiles above the fuel bed and the fuel bed height are measured. Pyrolysis gas is sampled with a cooled probe and analysed on its CO, CO2, CH4, VOC, H2O, H2 and O2 composition. The experiments show that drying occurs in the first third of the grate with a relatively constant release of water vapour from the fuel bed. The temperature of the dried fuel further increases on the grate. The release of volatiles from the fuel pyrolysis starts towards the end of the drying zone and occurs in a relatively narrow zone. The fuel bed simulations are validated, discussed and used to analyse the influence of parameters on the fuel conversion such as the moisture content of the fuel and the primary air distribution. The model forms a basis to calculate the entry conditions for subsequent gas phase simulations.

Effect of Gd and Nb on dielectric and magnetic transition temperature of BaTiO3- Li0.5Fe2.5O4 composites

The Gd and Nb doped 90 BaTiO3- 10 Li0.5Fe2.5O4 composites are prepared using solid state technique. The structural, functional, dielectric, magnetic and magneto-electric properties of Gd and Nb doped 90 BaTiO3- 10 Li0.5Fe2.5O4 have been studied using X-ray diffraction, FTIR, dielectric spectrometer, vibrating sample magnetometer and DSP lock-in amplifier respectively. The XRD peaks indicate the absence of impurities in the undoped and doped BLF composite which confirms the high crystalline nature of all the composites. The FTIR spectrum reveals a strong absorption bands at 468 cm−1 and 853 cm−1. The transition temperature of BLF decreases slightly and the dielectric constant of all composites is maximum for different temperatures at fixed frequency due to mechanical strain in the grains and inhomogeneous distribution of Gd and Nb ions in place of Ti. The dielectric dissipation (tan δ) of BLF decreases with increase in the concentration of Gd and Nb in BLF which indicates the less number of defects like oxygen vacancies in BLF. The magnetic transition increases with increase in the concentration of Gd and Nb in BLF composites and this increase of the magnetic transition may due to the presence of exchange interaction between Fe3+ and Gd 3+, Nb5+ ions through neighboring octahedrons. The M-E coefficient of BLF decreases after doping Gd, Nb in BLF which may be due to the resistivity of ferroelectric phase greater than ferrite phase.

Aluminum-Tailored Energy Level and Morphology of Co3- x Alx O4 Porous Nanosheets toward Highly Efficient Electrocatalysts for Water Oxidation.

Tuning energy levels plays a crucial role in developing cost-effective, earth-abundant, and highly active oxygen evolution catalysts. However, to date, little attention has been paid to the effect of using heteroatom-occupied lattice sites on the energy level to engineer electrocatalytic activity. In order to explore heteroatom-engineered energy levels of spinel Co3 O4 for highly-effective oxygen electrocatalysts, herein Al atoms are directly introduced into the crystal lattice by occupying the Co2+ ions in the tetrahedral sites and Co3+ ions in the octahedral sites (denoted as Co2+ Td and Co3+ Oh , respectively). Experimental and theoretical simulations demonstrate that Al3+ ions substituting Co2+ Td and Co3+ Oh active sites, especially Al3+ ions occupying the Co2+ Td sites, optimizes the adsorption, activation, and desorption features of intermediate species during oxygen evolution reaction (OER) processes. As a result, the optimized Co1.75 Al1.25 O4 nanosheet exhibit unprecedented OER activity with an ultralow overpotential of 248 mV to deliver a current of 10 mA cm-2 , among the best Co-based OER electrocatalysts. This work should not only provide fundamental understanding of the effect of Al-occupied different Co sites in Co3-x Alx O4 composites on OER performance, but also inspire the design of low-cost, earth-abundant, and high-active electrocatalysts toward water oxidation.

The oxidation effects on microstructure and mechanical behavior of the Csf/α- Al2O3 composites at 1000 °C

Effects of oxidation on fracture behavior, microstructure and mechanical properties of the short carbon fiber reinforced α-Al2O3 composites (Csf/α-Al2O3) were studied under 1000 °C in ambient atmosphere for up to 40 h. The Csf/α-Al2O3 composites with carbon fiber content of 5 vol% (denoted as Csf5) exhibit catastrophic fracture mode before and after oxidation. The Csf10 sample that has a pseudo-plastic fracture behavior exhibits catastrophic failure after only 0.5 h of oxidation. The retention strength of Csf/α-Al2O3 composites, apparently decreased with the increasing of oxidation time, is strongly influenced by the content of residual carbon fiber. After oxidation at 1000 °C for 0.5 h, the retention strengths of Csf5 and Csf10 composites are 300 MPa and 222 MPa, which are 89% and 90% of the original strength respectively. After 2 h of oxidation, the retention strengths of Csf5 and Csf10 are 242 MPa and 185 MPa, which are 72% and 69% of the original strength respectively. Oxidation process significantly affects the matrix morphology of Csf/α-Al2O3. A large amount of small grain appears and characterizes the matrices of Csf5 and Csf10 samples after 40 h of oxidation. The substrate grain refinement is ascribed to a process of carbothermal reduction nitridation reaction of Al2O3.

Down and up conversion luminescence of ZrTi (1+x)O4 nanocomposites by visible light absorption

A series of self-doped ZrTi (1+x)O4 (ZT) composites with x = 0, 0.2, 0.4, 0.6 and 0.8 M per cent are synthesized by solution combustion method. Occurrence of both stokes and antistokes luminescence under visible light absorption founds to be more interesting results of the present investigation. Optical characterization, Fourier-transform infrared spectroscopy, Raman spectroscopy (FTIR, RAMAN) and material characterization, Powder X-ray diffraction pattern (PXRD) confirms mixed phase of the compound. Scanning electron microscope (SEM) studies show well defined interfaces with spherically elongated rod like particles. Surface defects created by TiO2 and ZrO2 make interstitial energy levels available well within the band gap which act as deep trap levels accommodate visible light absorption with PL peaks on both stokes and antistokes shift is made possible.

Catalytic performance of transition metals (Co, Ni, Zn, Mo) doped CuO-Ce0.8Zr0.2O2 based catalysts for CO preferential oxidation in H2-rich streams

CuO-Ce0.8Zr0.2O2 composites (CuCZ) doped by transition metals (Co, Ni, Zn, Mo) as well as Co-doped CuCZ with different molar ratios of Co/Cu were prepared by a facile urea grind combustion (UGC) method and applied for CO preferential oxidation (CO-PROX) reaction in the hydrogen-rich gas mixtures. The characterizations of XRD, N2 adsorption-desorption, SEM, TEM, XPS and H2-TPR were used to investigate the difference in the catalytic behavior. Activity results found that the modification of Co had a positive influence on the catalytic activity of CuCZ and the optimal ratio of Co/Cu was 1/10, while the addition of Ni, Zn and Mo resulted in the decrease in the catalytic activities. XRD, SEM, H2-TPR and XPS results proved that the catalytic behavior of CuCZ based catalysts largely depended on the properties and types of transition metals. The addition of Co into CuCZ led to the isomorphous substitution of Cu2+ and Ce3+ species via Co2+ and Co3+, and the redispersion of Cu species over CeO2 support promoted the generation of the highly dispersed Cu oxides. As a result, large amount of active Cu+ sites and the surface active oxygen were available. The negative effects caused by Ni, Zn and Mo species were originated from the decreased amount of highly dispersed Cu oxides, possibly due to the differences in the oxidation-reduction property, the ion radius, the metal-support interaction as well as the nucleation rate and the size growth of particles during the preparation process. Consequently, the structure-property relationship was established, and the catalytic activity was suggested to be correlated with the amount of highly dispersed Cu oxides. Furthermore, 1/10Co-CuCZ showed excellent stability in terms of both CO conversion and CO2 selectivity during 120 h time-on-stream test.